There is known a suspension of a vehicle seat (cf., SU, A, No. 662,384) in which protection against vibration is ensured by adjusting the dynamic rigidity of resilient elements of the shock absorber. The resilient elements are made of lengths of a multicore cable having ends thereof secured between a support base and a movable shell secured on a post to be capable and a movable shell secured on a post to be capable of rotation about its own axis. The resilient elements are characterized by dynamic rigidity of a magnitude equal to the magnitude of the static rigidity. Variations in the angle of turn of the shell relative to the base lead to a change in the inclination angle of the cable lengths and dynamic rigidity of the resilient elements of the shock absorber.
Reduced dynamic rigidity of the resilient elements results in a reduction in the natural frequency of oscillations of the support of the vehicle seat. Due to the equality in the magnitudes of the dynamic and static rigidity of the resilient elements, adjustment of the dynamic rigidity influencing the efficiency of protection of the driver against vibrations of the vehicle gives rise to variations in the static rigidity of the resilient elements determining the static sagging of the support of the vehicle seat. Therewith, reduced dynamic rigidity of the resilient elements ensuring a more efficient protection against vibrations causes a reduction in the static rigidity of the resilient elements and consequently a more pronounced static sagging of the vehicle seat due to the weight of the operator.
Therefore, there is a conflict between the preferred reduction in the natural frequency of oscillations of the shock absorber for attaining a more reliable protection against vibrations and the magnitude of the allowable static sagging. Protection of the operator against vibrations of the vehicle he drives is thus limited by the allowable static sagging of the support element of the vehicle seat.
There is also known a suspension of a vehicle seat (cf., SU, A, No. 1,357,625) having the form of an adjustable vibrations insulator or absorber comprising a bearing plate to which the vehicle seat is secured, a first base mounted on the floor or the vehicle, mechanical resilient elements secured about the outer perimeter of the first base between the first base and bearing plate. Arranged in parallel with the mechanical resilient elements at the first base to extend vertically in line with its axis of symmetry is an electrodynamic exciter made up of a fixed system in the form of a magnetic circuit having an annular clearance and secured at the first base, and a movable system in the form of coils arranged in the annular clearance of the magnetic circuit. The static rigidity of the suspension is determined by the rigidity of the resilient elements, whereas the dynamic rigidity is determined by the rigidity of the resilient elements and rigidity imparted by the electrodynamic exciter, which can be either positive or negative depending on the flow of the direct current passing through the coils. The natural frequency of oscillations of the vehicle seat suspension can be increased if the rigidity imparted by the electrodynamic exciter is positive, or reduced if the imparted rigidity is negative. However, such an adjustment of the dynamic rigidity irrespective of the static rigidity is possible only when in the initial position prior to energizing the coils assume a definite position relative to the clearance in the magnetic circuit of the electrodynamic exciter, viz., the coils must be arranged in symmetry relative to a horizontal plane extending through the midpoint of the clearance of the magnetic circuit. In this case, during oscillations the upper and lower coils are caused to be alternately forced to the clearance of the magnetic circuit to a magnitude equalling the amplitude of oscillations whereby a pushing force is produced which is proportional to the relative displacement between the first base and bearing plate, i.e., a pushing force equivalent to the dynamic rigidity of the suspension. In the absence of oscillations the coils are brought out of the clearance of the magnetic circuit whereby they fail to provide a continuous pushing force which would be equivalent to the static rigidity. However, this manner of adjusting the rigidity of the vehicle seat suspension is possible only when under the action of the weight of the operator the static sagging of the suspension determined by the static rigidity of the resilient elements is such that the coils assume the heretofore described initial position. As the rigidity of the resilient elements is a constant, the required static sagging according to the known expression .delta.=P/k, where .delta. is the static sagging, P=mg is the gravity force, m is the mass of the driver, and k is the static rigidity of the vibrations insulator, is preset only for an operator of a certain weight. If the weight of the operator is other than that for which the seat is adjusted, the static sagging of the suspension is also different from the specified, and the coils fail to assume the required initial position. Therewith, one of the coils in the initial position accommodates in the clearance of the magnetic circuit, and as it is energized by a direct current source it produces a pushing force in the absence of vibrations in the vehicle. Depending on the flow of electric current, this pushing force acts to additionally compress or expand the resilient elements thereby changing the static sagging of the suspension, i.e., the effect of this pushing force is equivalent to the static rigidity of the resilient elements.
In view of the aforedescribed, the dynamic rigidity of the suspension can be adjusted without changing the static rigidity of the resilient elements only for an operator of definite weight. The weight of the drivers can vary within a wide range, and therefore the capability of adjusting the dynamic rigidity of the vehicle seat suspension is inherently limited to result in less efficient protection of the driver against vibrations of the vehicle.